Choline and ethanolamine are precursors for the phospholipids phosphatidyl choline, phosphatidylethanolamine, and sphingomyelin. The latter accounts for approximately two-thirds of the total phospholipid in the human lens. The choline enters the lens by means of a specific carrier and is phosphorylated by choline kinase. Phosphorylcholine accumulates in the lens and serves as an intermediate in the formation of phospholipids. The overall aim of this project includes the study of transport and metabolism of choline and ethanolamine in normal, photooxidatively damaged, and cataractous lenses. The specific aims include elucidation of the specificity and kinetic parameters of the lens choline carrier, lens choline kinase, and lens ethanolamine kinase. Because photooxidation has been shown to produce lens changes similar to those which occur in human senile cataract, and because lens choline metabolism is sensitive to photooxidative damage, the effects of photooxidation on lens choline metabolism will be further studied in animal lenses to determine the mechanism of this damage. The biochemistry of choline also may be altered in human senile cataracts which appear to have lower phosphorylcholine and phosphorylethanolamine concentrations than normal lenses. Therefore, human normal and cataractous lenses will be studied as well. transport phenomena will be studied in organ culture, homogenates, and partially purified enzyme preparations. Lenses or homogenates will be incubated with radiolabeled choline and/or ethanolamine, and the phosphorylated products will be separated from the unphosphorylated substrates by ion exchange and thin layer chromatography. Photodynamic damage to rat and rabbit lenses will be studied, and normal and cataractous human lenses will be compared, both to determine endogenous pool sizes for choline and ethanolamine metabolites and to follow the metabolism of added tracers. By study of the choline carrier and choline metabolism in lens, it may be possible to discover the mechanisms which control choline and ethanolamine metabolism. The study of changes in these biochemical processes in damaged or cataractous lenses may explain some of the metabolic events which occur during cataractogenesis and eventually suggest means of intervention to reverse or prevent these changes.